A declining number of Nevada residents are interested in working even as new jobs are created, and state researchers want to know more.Some of the decline may be a result of the recession, they say, because people who struggled to find work simply gave up and dropped out the labor force.But economists think that other, deeper changes also may developing in the economy of Nevada and other states across the nation.The phenomenon is getting increased attention partly because a permanent decline in the size of the workforce could carry big implications for employers who will be recruiting workers as the …